|“||Young man, I think you've got this coming to you!||”|
|— Mr. Webster to his grandson, before taking him over his knee for a spanking in the 1941 movie The Devil and Daniel Webster|
Young man (or young gentleman) is a mode of address typically used for boys of any age, but especially for preteens. It is roughly the male equivalent of "young lady". Occasionally the mode of address is also used for men in their twenties, but may offend people because of its belittling connotations.
The phrase comes with some irony when used for a child who is far from being a man. Although by itself friendly and not impolite, the title has certain subliminal connotations along the lines of "you are still a little boy" or "we expect you to behave like a gentleman (but you are behaving like an ill-mannered little boy)".
A boy is often addressed "young man" when he is reproved for misbehavior, e.g. by his mother, father, grandparent, governess, teacher, or any other authority. It is used in second person (e.g. "Young man, come here at once!") and in third person (e.g. "Can you give me a hand, darling? This young man needs to be taught a lesson.")
"Young man" is a popular phrase in spanking literature, spanking movies, and in spanking roleplay. Some male adult spankees love it when they are called "young man" in a stern voice to start some roleplay/spanking activity because these two simple words can be enough to raise a whole wave of emotions.